Most folks seem to use either 'Building' or 'in the garden'.
Often there is no obvious forum for some topics. For example, questions about central heating programmers and thermostats are sometimes posted under heating and sometimes electrics. It's a matter of choosing the one that you think the people with the relevant skills you need would read. So in your case, I would go for building which is probably more akin to drive construction. Gardens tends to be more about planting.